1. Field
One or more example embodiments relate to inkjet printing devices using a combination of a piezoelectric technique and an electrostatic technique, and methods of driving the same.
2. Description of the Related Art
Conventional inkjet printing devices eject fine droplets of ink onto desired positions of printing media by using inkjet heads to print given, desired or predetermined images on printing sheets. The inkjet printing devices have been applied to a larger variety of fields, for example, flat panel displays (FPDs) such as liquid crystal displays (LCDs) and organic light emitting displays (OLEDs), flexible displays such as electronic paper (e-paper), printed electronics such as metal interconnection lines, and organic thin film transistors (OTFTs). Among process techniques for applying the inkjet printing devices to display devices or printed electronics, relatively high-resolution ultrafine printing techniques may be needed.
Related art inkjet printing devices may be classified as piezoelectric inkjet printing devices and electrostatic inkjet printing devices depending on how the ink is ejected. Specifically, related art piezoelectric inkjet printing devices eject ink by deforming a piezoelectric material, while related art electrostatic inkjet printing devices eject ink using an electrostatic force. In more detail, related art electrostatic inkjet printing devices operate based on the following two methods. In a first method, ink droplets are ejected using electrostatic induction. In a second method, charged pigments are accumulated using an electrostatic force and then ink droplets are ejected.
In the case of a piezoelectric inkjet printing device, because ink is ejected by using a drop on demand (DOD) technique, it is relatively easy to control a printing operation and drive the inkjet printing device. Also, the piezoelectric inkjet printing device generates ejection energy by mechanically deforming a piezoelectric material, and thus, any kind of ink may be used. However, the piezoelectric inkjet printing device does not produce ultrafine droplets having a size of several picoliters or less nor does it allow ink droplets to reach a desired position as compared with an electrostatic inkjet printing device.
The electrostatic inkjet printing device may produce ultrafine droplets, is relatively easy to drive, and allows ink to be ejected in a desired direction. As a result, the electrostatic inkjet printing device is more appropriate for relatively precise printing processes. However, because it is difficult to form separate ink flow paths in an electrostatic inkjet printing device by using an electrostatic induction technique, ink is relatively difficult to eject via a plurality of nozzles by using the DOD technique. Also, when charged pigments accumulate due to an electrostatic force, the ejection rate of ink droplets and the kind of ink is limited because it is necessary to accumulate relatively highly dense pigments.
Moreover, in the related art the amount of ejected ink droplets is proportional to the diameters of nozzles of inkjet printing devices. Thus, it is necessary to reduce the sizes of nozzles to eject fine ink droplets. However, a reduction in the sizes of the nozzles makes it difficult to manufacture precise nozzles and causes the nozzles to clog more frequently, thereby reducing reliability.